[R-390] Grounds

[ToddRoberts2001 at aol.com]

In a message dated 7/29/2009 4:45:45 P.M. Eastern Daylight Time,  
dmetz at ntelos.net writes:

So,.... my question is: if we have additional grounds for our  
equipment, are we safer or more in danger if we do not connect them to  
the service entrance ground. Perhaps this is beyond the scope of this  
reflector but it seems like we have some engineers lurking in the  
background and I would really appreciate the science of this anomaly  
when talking about grounds to the entire  group.

73's
Dave
Kj4JX
 
_______________________________________________
 
As I understand it, there is more danger if the added grounds are not
connected together with heavy-gauge wire to the service entrance  ground,
and with minimal sharp bends to the wire.  This is because of the 
ground resistance between the separate grounds. For example if you
provide a separate ground rod for your R-390A located in a back room,
say 50 feet away from the entrance ground rod. If lightning hits  nearby,
the extremely high current traveling along the ground can create a large  
voltage-drop
between the two ground rods of thousands of volts, even if the  lightning
is not a direct hit. This can cause your isolated ground rod to be at a 
potential of thousands of volts in relation to your house ground and  home
wiring third-wire ground.
 
If the ground rods are tied together then the potential difference may be 
close to zero or perhaps only a few volts depending on how much current  
flows 
along the ground from the nearby hit. 
 
Always safest to simply unplug the radio itself and disconnect it from  any 
external connections, antenna and ground, during a thunderstorm to  avoid
these problems.  An isolated ground rod can be dangerous in a nearby  hit.
A cable company ground should be connected to your service entrance ground 
for best safety.
 
73 Todd WD4NGG
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